1. Technical Field
The present invention relates in general to mechanical fasteners and, in particular, to an improved system, method, and apparatus for removing failed fasteners from structures that are fabricated from composite materials.
2. Description of the Related Art
Some structures, such as the wing skins of high performance aircraft, are formed from composite materials rather than from metals or metal alloys. Composite materials offer a number of advantages over metals, such as a very high strength to weight ratio. Composite materials also have some disadvantages, including lower hardness and durability compared to metallic materials. Because of these disadvantages, composite materials are not suitable for use as all structural components. For example, metallic fasteners (e.g., bolts, screws, etc.) are required to join some structural elements.
Unfortunately, even metallic fasteners are capable of failing due to improper installation or extended service over time. There is a conventional procedure for removing a failed fastener from composite materials. This approach requires a technician to hand-drill a pilot hole in the failed fastener, and then remove the fastener with a conventional tool that is commonly referred to as an “EZ-Out.”
This conventional removal procedure does not always work. When this method fails, the technician must drill out the failed fastener at an even deeper level until the head of the fastener breaks off from the threaded portion of the bolt. Where and how the head breaks off from its shank is very unpredictable. Such fastener breakage often leaves sharp burrs on the fastener shank that must be pulled through the composite materials. The sharp burrs cause damage to the inner surfaces of the hole that the fastener was in. The damaged hole must then be repaired or re-worked to accept an oversized fastener at considerable additional cost.
Currently, this process requires technicians with the highest level of skill available. All of the foregoing drilling and repair operations are performed “free hand” with little or no radial support or rigid guidance for the precise control and alignment of the cutting tools used. Such operations may be relegated to the mechanics on the shop floor using whatever tools and/or methods they are comfortable with. As a result, there is a high level of variation in the success and quality of the operations performed. Thus, an improved system, method, and apparatus for removing failed fasteners from structures would be desirable.